Recently, a light emitting device using a light emitting diode (LED) and a phosphor has been proposed in order to miniaturize a projector.
Patent Literature 1 describes a fluorescent wheel for a projector, which can be produced by providing a ring-like phosphor layer and a transparent material layer on a ring-like rotatable transparent substance, and a light emitting device. Further, Patent Literature 1 describes, as the phosphor layer, one kind or more of phosphor selected from an oxide phosphor, a nitride phosphor, an oxynitride phosphor, a chloride phosphor, an oxychloride phosphor, a sulfide phosphor, an oxysulfide phosphor, a halide phosphor, a chalcogenide phosphor, an aluminate phosphor, a halophosphoric acid chloride phosphor, and a garnet-based compound phosphor, and as the transparent material layer, a glass matrix of borosilicate based glass, phosphate based glass or the like, and describes that a content of the phosphor is 5 to 80 vol %.
In the phosphor layer and the transparent material layer described in Patent Literature 1, it is intended to radiate heat from the phosphor due to use of the transparent substrate having high thermal conductivity. However, the effect of heat radiation is not satisfactory because glass having low thermal conductivity is used in the phosphor layer. Therefore, there is a problem that light emission efficiency deteriorates due to heat generation of the phosphor.
In addition, the content of the phosphor is as low as at most 80%, and therefore, excitation light cannot be absorbed satisfactorily. Thus, there is another problem in conversion efficiency.